In a typical liquid chromatograph (hereinafter, referred to as “LC”), a mobile phase stored in a mobile phase container is drawn by a liquid-feeding pump and fed to a column through a sample injector. When a sample liquid is injected from the sample injector into the mobile phase at a predetermined timing, the sample liquid is washed out by the mobile phase, to be introduced into the column. While the sample liquid passes through the column, various components in the sample liquid are separated in a time direction so as to be eluted from the outlet of the column. The components contained in the eluate are detected by a detector, such as a photodiode array (PDA) detector, which generate detection signals individually corresponding to the concentrations of the components. Based on the detection signals, a chromatogram is created which indicates the change in the signal intensity along with time.
In such an LC, the mobile phase fed by the liquid-feeding pump under high pressure may contain a large quantity of gas that may cause bubbles to occur in the column or a cell in the detector. Such bubbles are one of the factors for a deformation of the peak or an occurrence of spike noises in the chromatogram. Furthermore, a change in the quantity of gas (mainly oxygen) dissolved in the mobile phase that arrives at the detector also causes a fluctuation or drift of the baseline in the chromatogram. In addition, if bubbles occur in the mobile phase container or other locations and are fed into the liquid-feeding pump, those bubbles may cause defectiveness in the liquid-feeding operation by the pump, causing a change in the retention time of the peak or other problems. In order to reduce such adverse effects on the analysis results, a conventional LC includes a degassing device in the passage between the mobile phase container and the liquid-feeding pump, for removing air and/or bubbles dissolved in the mobile phase.
There are several systems for degassing. One of the widely used systems is a reduced-pressure degassing system using a gas-liquid separation membrane. As disclosed in Patent Literature 1 and Non Patent Literature 1, a degassing device that employs such a system (hereinafter, a degassing device that employs the reduced-pressure degassing system using a gas-liquid separation membrane is simply referred to as a “degassing device”) includes a degassing tube contained in a vacuum chamber evacuated (or pressure-reduced) by a vacuum pump, which tube is made of a gas-permeable material (such as polytetrafluoroethylene (PTFE)-based synthetic resin) that allows gas to pass through while preventing the passage of liquid. When a mobile phase drawn from the mobile phase chamber flows through the degassing tube, the air dissolved in the mobile phase is extracted into a vacuum atmosphere through the wall surface of the degassing tube made of the gas-permeable material. Thus, the air in the mobile phase is removed.
If an abnormality has been found in a measurement result obtained by an LC system using the aforementioned degassing device, the cause of the abnormality may possibly be degradation in the degassing performance of the degassing device. Meanwhile, when high measurement accuracy is required, a high level of degassing performance is necessary since even a few bubbles can cause problems. In view of the above, it may be necessary to verify the degassing performance of the degassing device at an appropriate timing. In a typical method for verifying the degassing performance of the degassing device, the absorbance of the mobile phase is measured in each of the two cases where the mobile phase is passed through the degassing device and where the mobile phase is not passed through, using an ultraviolet (UV) visible light spectrophotometer, and the degassing performance is determined based on a change in the absorbance between the two cases.